Proceedings Paper

We characterize the geometry and electronic structure of isomers of the five atom Manganese cluster for its highest spin state, multiplicity 26. DFT calculations with various functionals and basis sets. The lowest energy form is either a D3h symmetric trigonal bipyramid or disphenoid C2v structure which can be considered a distorted trigonal bipyramid. The regular pentagon (D5h) is higher in energy but occupies a shallow relative minimum on the potential surface. The lowest energy square pyramid (C4v) is a saddle point; it spontaneously rearranges to the bisphenoid structure or the trigonal bipyramid very similar in energy. Analysis of the wave functions shows that the clusters can be considered distinct and weakly bound atoms with stabilization derived from interatomic charge-transfer interactions. Dispersion attraction seem to play a lesser role. The clusters have moderate static polarizabilities α but large first hyperpolarizabilities β, comparable with the reference system para-nitro aniline. Dynamic polarizabilities for an exciting frequency of 0.1 atomic units (wavelength 450 nm) are higher still.